1. Field of the Invention
This invention relates to an interlock for mechanically preventing two electromagnetic switches from being turned on at the same time, and has particular application to forward and reverse controllers for electric motors.
2. Background Information
There are applications were two electromagnetic switches must not be energized at the same time. One such application involves the forward and reverse controllers for electric motors. Simultaneous operation of both controllers would result in short circuiting of the phases of the power supply.
There are a variety of mechanical interlock designs in use today for preventing the simultaneous energization of two controllers. Probably the most common type of mechanical interlock is the "see saw" design. This type of interlock relies on the high closed gap force of an electromagnet compared to the open gap force to prevent the closure of the second controller. However, it is possible to cause a transition from a primary controller to a secondary controller by the application of an external mechanical force. Also, the linear nature of this design results in substantial travel of both controllers before interlocking action begins. Another common mechanical interlock is based on using a "four bar" linkage. An example of such an interlock is disclosed in U.S. Pat. No. 3,815,063. The "four bar" design eliminates the long pretravel of the "see saw" design, but a transition from a primary controller to a secondary controller can still be forced mechanically.
There is a need for an improved mechanical interlock for a pair of electromagnetic switches.
There remains a need for a mechanical interlock for a pair of electromagnetic switches which can not be overridden by application of a mechanical force.
There is also a need for such an improved mechanical interlock which provides the interlock function with minimum travel of the switch armatures.
There is a continued need for such mechanical interlocks which are rugged, reliable, and economical to manufacture and retrofit to existing electromagnetic switches.
There is a particular need for such an improved interlock adapted for interlocking forward and reverse motors controllers.